Conventionally, there is a sealed battery hermetically sealed in a manner that an electrolyte is poured in a battery case enclosing an electrode body and then a liquid inlet is sealed. One example of secondary batteries using a flat rectangular metal battery case is formed with a liquid inlet in a lid member that closes an opening of the battery case. When such a battery is to be manufactured, a lid member with a liquid inlet opened is fixed to a battery case before an electrolyte is poured therein, and then the electrolyte is injected in the battery case through the liquid inlet. After liquid pouring, a metal sealing plate is placed to cover the liquid inlet, and the circumference of the sealing plate is welded to the lid member without gap. Thus, a sealed battery is produced.
Patent document 1 discloses a sealed battery configured such that a liquid inlet is sealed with a sealing plug formed of a metal plate combined with a resin protruding portion, not a simple plate-like sealing plate. According to Patent Document 1, a burr protrusion is formed in the liquid inlet, so that the protruding portion is temporarily fixed in the liquid inlet by insertion therein. Accordingly, the sealing plug is less likely to be displaced in the course of welding the metal plate to a battery housing, thereby enabling reliably preventing sealing defects. Patent Document 1 teaches, as one example of the material of the protruding portion, rubber material having appropriate elasticity and others.